108 CLASSIFICATION OF MINEBALS. 



the absence or presence of the metallic lustre ; or by the 

 assay becoming, or not becoming, magnetic after roasting. 



The third class, the earthy minerals, are divided into three 

 orders : First, those that are soluble, wholly, or in consider- 

 able proportion, in cold, diluted muriatic acid. Secondly, 

 those fusible before the blowpipe. Thirdly those infusible. 

 The first order is not divided into genera and families. The 

 second and third orders are divided into several genera, the 

 characteristics of which are their different degrees of hard- 

 ness ; and these degrees of hardness are characterised by the 

 minerals, first, scratching quartz with ease ; secondly, scratch- 

 ing quartz with some difficulty, and scratching feldspar with 

 ease ; thirdly, being as hard, or harder, than feldspar ; being 

 scratched by quartz, and scratching window glass with ease ; 

 fourthly, being softer than feldspar; scratching fluor, and 

 scratching window glass feebly ; fifthly, being scratched by 

 fluor spar. 



The fourth class, or the saline minerals, are divided into 

 two orders, the characteristics of which are, the giving or 

 not giving, when in solution, a precipitate with carbonated 

 alkali. These orders are not divided into genera and fami- 

 lies, the minerals composing them being few and easily 

 distinguished. 



By pursuing the various branches of inquiry which we have 

 thus pointed out, by studying first, the principles of crystallo- 

 graphy ; next, the external characters of minerals ; and by 

 directing his attention, lastly, to their chemical relations, 

 the student will, by insensible degrees, acquire a highly 

 valuable acquaintance with this interesting science, and will 

 soon be able to effect the essential objects of identifying the 

 various mineral substances submitted to his inspection, and 

 of connecting their occurrence with the respective deposits 

 in which they are found with the general structure and past 

 history of the earth. In short, he will speedily be enabled 

 to acquire a sufficient knowledge of the subject for every 

 purpose of geological investigation. 



